Wireless underground radio signal emitting nodes have been employed for monitoring soil parameters over longer periods of time. Said nodes are commonly also referred to as “soil scouts” and find various applications in agricultural applications. The nodes are employed to monitor, for example moisture or temperature using the corresponding sensors. However, since they are buried underground, mostly on fields or other agricultural zones, a lot of effort has been made in the past to properly transmit the measurement data of the sensors to a radio station or a radio unit collecting the measurement data at certain time intervals over a longer period of time, like months or even years.
In the focus of research and development was typically the high attenuation caused by the soil and its effects on the design of the antennas. Since the node has to be installed just below the ploughing depth or a depth that is sufficient to protect it, a considerable radio emission power has to be employed in order to transmit the measurement data through the soil and also through the air in order to reach the radio station or any other radio unit collecting the measurement data.
In the research paper “Validation and results of the soil scout radio signal attenuation model”, Biosystems Engineering 97 (2007) 11/19 by J. Tiusanen the above mentioned problems of under soil monitoring in agriculture were already considered. It was recognized that a node with a convenient range of operation would need to emit with a power, which would violate radio band regulations.